Many of the developing countries produce huge quantities of agro residues but they are used inefficiently causing extensive pollution to the environment. The major residues are rice husk, coffee husk, coir pith, jute sticks, bagasse, groundnut shells, mustard stalks and cotton stalks. Sawdust, a milling residue is also available in huge quantity. Apart from the problems of transportation, storage, and handling, the direct burning of loose biomass in conventional grates is associated with very low thermal efficiency and widespread air pollution. The conversion efficiencies are as low as 40% with particulate emissions in the flue gases in excess of 3000 mg/ Nm³ In addition, a large percentage of unburnt carbonaceous ash has to be disposed of. In the case of rice husk, this amounts to more than 40% of the feed burnt. As a typical example, about 800 tonnes of rice husk ash are generated every day in Ludhiana (Punjab) as a result of burning 2000 tonnes of husk. Briquetting of the husk could mitigate these pollution problems while at the same time making use of this important industrial/domestic energy resource.
Historically, biomass briquetting technology has been developed in two distinct directions. Europe and the United States has pursued and perfected the reciprocating ram/piston press while Japan has independently invented and developed the screw press technology. Although both technologies have their merits and demerits, it is universally accepted that the screw pressed briquettes are far superior to the ram pressed solid briquettes in terms of their storability and combustibility. Japanese machines are now being manufactured in Europe under licensing agreement but no information has been reported about the manufacturing of European machines in Japan.
Worldwide, both technologies are being used for briquetting of sawdust and locally available agro-residues. Although the importance of biomass briquettes as substitute fuel for wood, coal and lignite is well recognized, the numerous failures of briquetting machines in almost all developing countries have inhibited their extensive exploitation.
Briquetting technology is yet to get a strong foothold in many developing countries because of the technical constraints involved and the lack of knowledge to adapt the technology to suit local conditions. Overcoming the many operational problems associated with this technology and ensuring the quality of the raw material used are crucial factors in determining its commercial success. In addition to this commercial aspect, the importance of this technology lies in conserving wood, a commodity extensively used in developing countries and leading to the widespread destruction of forests.
Biomass densification, which is also known as briquetting of sawdust and other agro residues, has been practiced for many years in several countries. Screw extrusion briquetting technology was invented and developed in Japan in 1945. As of April 1969, there were 638 plants in Japan engaged in manufacturing sawdust briquettes, known as 'Ogalite', amounting to a production of 0.81 MTY. The fact that the production of briquettes quadrupled from 1964 to 1969 in Japan speaks for the success of this technology. This technology should be differentialed from such processes as the 'Prest-o-log' technology of the United States, the 'Glomera' method in Switzerland and the 'Compress' method in West Germany.
At present two main high pressure technologies: ram or piston press and screw extrusion machines, are used for briquetting. While the briquettes produced by a piston press are completely solid, screw press briquettes on the other hand have a concentric hole which gives better combustion characteristics due to a larger specific area. The screw press briquettes are also homogeneous and do not disintegrate easily. Having a high combustion rate, these can substitute for coal in most applications and in boilers.
Briquettes can be produced with a density of 1.2 g/cm³ from loose biomass of bulk density 0.1 to 0.2 g / cm³ These can be burnt clean and therefore are eco-friendly arid also those advantages that are associated with the use of biomass are present in the briquettes.
With a view to improving the briquetting scene in India, the Indian Renewable Energy Development Agency (IREDA) - a finance granting agency - has financed many briquetting projects, all of which are using piston presses for briquetting purposes. But the fact remains that these are not being used efficiently because of their technical flaws and also due to a lack of understanding of biomass characteristics. Holding meetings with entrepreneurs at different levels, providing technical back-up shells and educating entrepreneurs have to some extent helped some plants to achieve profitability and holds out hope of reviving the briquetting sector.
In other Asian countries although briquetting has not created the necessary impact to create confidence among entrepreneurs, recent developments in technology have begun to stimulate their interest. In Indonesia, research and development works (R&D) have been undertaken by various universities, the national energy agency and various research institutes since the mid-seventies. So far, these have mainly focussed on biomass conversion technologies. R&D works on biomass densification development are relatively rare. There are a number of export-oriented sawdust and coconut shell charcoal briquette producers. At present, densified biomass, particularly that which is not carbonized, is not a popular fuel in the country. A limited amount of smokeless charcoal briquettes, mostly imported, are consumed in some households of big cities. However, the prospects for the densified biomass industry in Indonesia, particularly where it is export oriented, seems to be good.
The Phillipine Department of Energy is currently promoting the development and widespread use of biomass resources by way of encouraging the pilot-testing, demonstration and commercial use of biomass combustion systems, as well as gasification and other systems for power, steam and heat generation. There is a limited commercial production of biomass briquettes in the country. At present nine commercial firms produce amounts ranging from 1 ton/day to 50 tons/day. Four pilot briquetting plants have stopped operation. Briquettes are produced from sawdust, charcoal fines and/or rice husk. In the Philippines the conversion cost from biomass to briquette is very high.
In Sri Lanka no briquetting projects have been implemented because of lack of exposure to the technology. But the prospects for substituting wood are high because the traditional sector relies heavily on fuel wood. The tea industry is the largest firewood consumer and it is supplied mainly from nearby rubber plantations or forests.
In Vietnam people have been involved in briquetting, but for limited uses. The briquettes are used basically for heating/cooking purposes and this is limited to households. The present non-commercial energy, mainly from biomass fuel, shares a great part of the total energy supply. R&D efforts should be undertaken to make briquetting technology economically profitable and socially acceptable to the public so that it might be widly adopted.
Briquetting plants with both small and high production capacities can be found in Thailand and, in general, plant performance in terms of profitability and management is encouraging. They have been successful in briquetting rice husk commercially. In other countries bottlenecks in the technology are the major reasons why briquetting is not popular. In Nepal small production capacity briquetting machines are currently operating and these can pave the way for large commercial production of briquettes which could make use of the huge quantity of agro-residues available in the country. In Bangladesh and Pakistan, although agro-residues are abundantly available, they are not used in briquetting.
Efforts have been made in Myanmar to reduce pressure on fuelwood and charcoal production. The government is providing support to state-run and private organizations to promote briquetting. The entrepreneurs, especially, are very much interested in briquetting of agro-residues and their utilisation.
India is the only country where the briquetting sector is growing gradually in spite of some failures. As a result of a few successes and IREDA's promotional efforts, a number of entrepreneurs are confidently investing in biomass briquetting. These entrepreneurs are also making strenuous efforts to improve both the production process and the technology.
Both national and international agencies have funded projects to improve the existing briquetting technology in India. Recently, the Indian Institute of Technology, Delhi in collaboration with the University of Twente, the Netherlands carried out research to adapt the European screw press for use with Indian biomass. The two major impediments for the smooth working of the screw press -- the high wear of the screw and the comparatively large specific power consumption required --were overcome by incorporating biomass feet preheating into the production process. The recent successes in briquetting technology and the growing number of entrepreneurs in the briquetting sector, are evidence that biomass briquetting will emerge as a promising option for the new entrepreneurs and other users of biomass.
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